An Optical Transport Network (OTN) is comprised of a plurality of switch nodes linked together to form a network. The OTN includes an electronic layer and an optical layer. The electronic layer and the optical layer each contain multiple sub-layers, further described herein. OTN structure, architecture, and modeling are further described in the International Telecommunication Union recommendations, including ITU-T G.709, ITU-T G.872, and ITU-T G.805, which are well known in the art. In general, the OTN is a combination of the benefits of SONET/SDH technology and dense wavelength-division multiplexing (DWDM) technology (optics).
The construction and operation of switch nodes (also referred to as “nodes”) in the OTN is well known in the art. In general, the nodes of an OTN are generally provided with a control module, input interface(s) and output interface(s). The control modules of the nodes in the OTN function together to aid in the control and management of the OTN. The control modules can run a variety of protocols for conducting the control and management (i.e. Operation, Administration and Maintenance—referred to as OAM) of the OTN. One prominent protocol is referred to in the art as Generalized Multiprotocol Label Switching (GMPLS).
Generalized Multiprotocol Label Switching (GMPLS) is a type of protocol which extends multiprotocol label switching (MLS) to encompass network schemes based upon time-division multiplexing (e.g. SONET/SDH, PDH, G.709), wavelength multiplexing, and spatial switching (e.g. incoming port or fiber to outgoing port or fiber). Multiplexing is when two or more signals or bit streams are transferred over a common channel.
Wave-division multiplexing is a type of multiplexing in which two or more optical carrier signals are multiplexed onto a single optical fiber by using different wavelengths (that is, colors) of laser light.
Lightpaths are optical connections carried over a wavelength, end to end, from a source node to a destination node in an optical transport network (OTN). Typically, the lightpaths pass through intermediate links and intermediate nodes in the OTN. At the intermediate nodes, the lightpaths may be routed and switched from one intermediate link to another intermediate link. In some cases, lightpaths may be converted from one wavelength to another wavelength at the intermediate nodes.
An exemplary OTN may contain multiple optical nodes, such as optical line terminals (OLTs), optical crossconnects (OXCs), optical line amplifiers, optical add/drop multiplexer (OADMs) and/or reconfigurable optical add/drop multiplexers (ROADMs), interconnected by way of intermediate links. OLTs may be used at either end of a connection or intermediate link. OADM/ROADMs may be used to add, terminate and/or reroute wavelengths or fractions of wavelengths. Optical nodes are further described in U.S. Pat. No. 7,995,921 titled “Banded Semiconductor Optical Amplifiers and Waveblockers” and U.S. Pat. No. 7,394,953 titled “Configurable Integrated Optical Combiners and Decombiners”, which are incorporated herein by reference in their entirety.
As previously mentioned, optical transport networks (OTN) have multiple layers including an electronic layer and an optical layer. The electronic layer includes an optical channel transport unit (OTU) sub-layer and an optical channel data unit (ODU) sub-layer. The optical layer has multiple sub-layers, including the Optical Channel (OCh) layer, the Optical Multiplex Section (OMS) layer, and the Optical Transmission Section (OTS) layer. The optical layer provides optical connections, also referred to as optical channels or lightpaths, to other layers, such as the electronic layer. The optical layer performs multiple functions, such as monitoring network performance, multiplexing wavelengths, and switching and routing wavelengths. The Optical Channel (OCh) layer manages end-to-end routing of the lightpaths through the optical transport network (OTN). The Optical Multiplex Section (OMS) layer network provides the transport of optical channels through an optical multiplex section trail between access points. The Optical Transmission Section (OTS) layer network provides for the transport of an optical multiplex section through an optical transmission section trail between access points. The OCh layer, the OMS layer, and the OTS layer have overhead which may be used for management purposes. The overhead may be transported in an Optical Supervisory Channel (OSC).
The Optical Supervisory Channel (OSC) is an additional wavelength that is adapted to carry information about the network and may be used for management functions. The OSC is carried on a different wavelength than wavelengths carrying actual data traffic and is an out-of-band channel. Typically, the OSC is used hop-by-hop and is terminated and restarted at every node.
A Super-Channel (SCh) is a collection of one or more frequency slots to be treated as a unified entity for management and control plane purposes. A Frequency Slot is a range of frequency allocated to a given channel and unavailable to other channels within the same flexible grid. A frequency slot is a contiguous portion of the spectrum available for an optical passband filter. A frequency slot is defined by its nominal central frequency and its slot width. A frequency slot is further defined in the International Telecommunications Union Recommendation ITU-T G.694.1, “Spectral grids for WDM applications: DWDM frequency grid”.
A contiguous spectrum Super-Channel is a Super-Channel with a single frequency slot. A split-spectrum Super-Channel is a Super-Channel with multiple frequency slots.
The International Telecommunications Union (ITU) recommendation ITU-T G.709 further defines the OTS, OMS and OCh layers and recommends use of the OSC to carry overhead corresponding to the layers. Additionally, ITU-T recommendation G.872 specifies defects for the OTS, OMS, and OCh layers as well as specifying Operation, Administration & Maintenance (OAM) requirements.
ITU-T recommendations suggest that the OSC utilize a Synchronous Transport Signal (STS) Optical Carrier transmission rate OC-3. Optical Carrier transmission rates are a standardized set of specifications of transmission bandwidth for digital signals that can be carried on fiber optic networks. The OC-3 frame contains three column-interleaved STS Level 1 (STS-1) frames; therefore, the line overhead consists of an array of six rows by nine columns (that is, bytes). The OC-3 frame format is further defined in Telecordia's Generic Requirements GR-253, “Synchronous Optical Network Common Generic Criteria,” Issue 4. The OC-3 frame format contains a transport overhead portion. Within the transport overhead portion, bytes designated as D4, D5, D6, D7, D8, D9, D10, D11, and D12 are defined by GR-253 for use by Data Communication Channel (DCC).
However, the mechanisms and protocols to carry Operation, Administration, and Maintenance (OAM) information over the OSC are not defined. A method is needed for supporting OAM functions for the optical layers, for example, for carrying defect information and overhead in the OSC.
The present disclosure addresses these deficiencies with methodology and apparatus for supporting OAM functions such as continuity, connectivity and signal quality supervision for optical layers. Specifically, the methodology discloses mapping optical layer overhead OAM information to specific overhead bits and assigning the overhead bits to specific OSC overhead bytes. This provides reliable exchange of overhead bytes over OSC between nodes. This methodology may be applied to Super Channel (SCh) connections as well as Optical Channels (OCh). Status information carried in the overhead may be used for restoration purposes in the optical transport network. The status information may also be used in support for tandem connection monitoring (TCM) configurations.